This invention relates to a sheet-wound transformer in which sheet conductors are wound into coils of required turns with an insulating sheet interposed between adjacent turns and cooling panels are provided at desired positions in the coils.
It is widely known that sheet-wound transformers are advantageous because the space factor of the conductors, that is, the ratio of the space occupied by the sheet conductors within the coils can be selected to a large value, and hence, the size and weight of the transformer can be substantially smaller than those of a conventional wire-wound transformer. However, in an application of high voltage and large capacity, it is essential to improve the cooling capability and assuring a high insulation. For this purpose, the transformer is provided with a plurality of cooling panels through which a coolant is circulated so that the heat generated in the conductors can be removed directly out of the conductors.
A sheet-wound transformer of a conventional construction comprises a magnetic core and a low-voltage coil and a high-voltage coil wound around the magnetic core with a sheet of insulating material interposed between each adjacent turns of the sheet conductor. The transformer further comprises a plurality of cooling panels each made into a hollow substantially rectangular construction wound or bent into an arcuate configuration. Inlet and outlet pipes are connected to appropriate portions of the panel for circulating a coolant therethrough. A plurality of spacers or ribs are provided in each panel for maintaining a proper spacing between the walls of the panel for coolant flow. Void space internally of the transformer tank is filled with an insulation gas such as SF.sub.6.
With the above described construction of the sheet-wound transformers, however, due to leakage magnetic fluxes, eddy currents have been generated at the upper and lower end portions (widthwise end portions) of the sheet conductors in the same direction as the load current, so that the current density at the portions is increased to a value more than seven times larger than the average value. This implies that Joule heat generated per unit time and unit volume of the conductor at these portions is approximately 50 times larger than the average value. However, due to the heat conduction in the axial direction (widthwise direction), the amount of heat to be removed (or cooled) out of the end portions is reduced to three times of the average value.
In the conventional construction of the sheet-wound transformers, since the ribs or spacers provided in each panel have been distributed evenly in parallel with each other with the leading ends and trailing ends thereof being aligned vertically. Thus the heat generated in the end portions of the conductor cannot be dissipated effectively, and local temperature rise in these portions could not be prevented.